A non-mechanical inertialess optical scanner is a critical building block in numerous optical applications ranging from laser communications, optical switching, model reconstruction, optical storage, and displays. Scanners need to be able to operate in one dimension (1-D), two dimensions (2-D), or three dimensions (3-D). The application requirements for an inertialess optical scanner, the high beam setting speed (e.g., in microseconds), a large number of scan beams, and simplicity in control electronics, are very attractive features for a scanner.
Three main approaches have evolved to form 1-D and 2-D type random access inertialess scanners. One approach uses two 1-D acousto-optic deflectors(AODs) or two 1-D electro-optic deflectors in cascade to form a beam that can scan in 2-D. See M. Gottleib, C. L. M. Ireland and J. M. Ley, "Electro-Optic and Acousto-Optic Scanning and Deflection," Marcel Dekker, 1983.
These approaches have the features of microsecond regime beam reset times and a moderately high, (i.e. 400.times.400 for the AOD-based scanner) scan spots. The limitations of these approaches include low (i.e. 20%) optical throughput efficiency, watt level high power and cost, radio frequency (RF) drive electronics, and limited beam acceptance aperture size(i.e. 1 cm.times.1 cm) for the scanner.
The second approach is via two large area multi-pixel birefringent-mode nematic liquid crystal devices (BM-NLC) that exhibit a highly desirable longitudinal electro-optical (EO) effect. See P. F. McManamon, T. A. Dorschner, D. L. Corkum, L. J. Friedman, D. S. Hobbs, M. Holz, S. Liberman, H. Q. Nguyen, D. P. Resler, R. C. Sharp, and E. A. Watson, "Optical Phased Array Technology," Proc. IEEE, Vol.84, pp. 268-298, Feb. 1996. This approach includes larger scan beam aperture size (i.e. 10 cm.times.10 cm) and the high degree of wave front programmability, both due to the large area, very large pixel count (i.e. million), design of NLC device technology. The limitations of this approach include the slow several milliseconds beam reset time due to the NLC devices, and the cost and complexity of the NLC million pixel drive electronics that includes a personal computer. Speed improvements can be made using a faster response EO material such as lead lantanum zirconate (PLZT), although at the cost of using high voltage (i.e. 400 Volts) control electronics and high complexity onchip electrodes due to the transverse EO effect exhibited by PLZT. Another problem associated with theses NLC/PLZT scanner devices is that an N-point 1-D deflection requires an N-pixel 1-D device that is driven by N independent electrodes with N independent voltage levels. Hence, as N gets large, e.g. 1000, the electronics get bigger and more costly.
An approach to solving the multi-signal drive problem was the use of an on-chip hardwired resistor network that formed a three terminal device. See N. A. Riza and M. C. DeJule, "Three terminal adaptive nematic liquid crystal lens device," Optics Letters, Vol. 19 No. 14, pp. 1013-15, July, 1994. In this case, for an NLC device, a simple variation of a single low voltage (1-3V) device drive signal allowed the device to step through its various beam forming settings. Another limitation of this approach is due to its hardwired device control structure, as it takes away almost all the degrees of freedom available in a multipixel drive device. Hence, if total programming flexibility is required, the on-chip hardwired approach is not suitable. A compromising approach recently proposed using PLZT devices is to use two independently driven 1-D scan devices. See J. A. Thomas, M. E. Lasher, Y. Fairman, P. Soltan, "PLZT-based dynamic diffractive optical element for high speed random access beam steering," SPIE Proc., Vol. 3131, No 13. Jul. 27-Aug., 1997. In other words, two 32 electrode devices placed in cascade can provide 32.times.32 or 1024 scan spots, then we only need to control 64 voltage levels, not 1024 voltage levels, as previously needed in a single multi-pixel drive 1-D scanner device. The group has proposed forming a 2-D scanner, by orthogonally placing the x and y-direction PLZT deflector devices in a cascaded geometry. Hence, for a 1024.times.1024 point 2-D scan, four PLZT 32-electrode drive signal devices are needed that require 128 independently controlled voltage levels. Although this approach has its advantages in terms of reduction in number of scanner control signals, the complexity of the proposed PLZT devices in terms of device parameters such as a demanding electrode design for a transverse EO effect material, high voltage (e.g., 100 V) drive signals, and limitations in a device optically active area, impose key restrictions towards achieving a low cost high speed 2-D scanner.
The third most recent approach for forming a 1-D or 2-D scanner is by using tiny micro mirror devices. See D. A. Francis, M. H. Kiang, O. Solgaard, K. Y. Lau, R. S. Muller, and C. J. Chang-Hasnain, "Compact 2-D laser beam scanner with fan laser array and Si micromachined microscanner," IEE Electronics Letters, Vol. 33, No. 13, Jun. 19, 1997.
The key limitation of these micro mirror approaches is their non-solid state nature, leading to moving parts with critical wear and tear and reliability issues.
Because theses spinning optics are bulky and slow, present 3-D scan systems are not completely solid-state and inertialess and cannot implement rapid 3-D scans. Hence, the ultimate goal of the scanner industry is to realize a low cost, 3-D inertialess, low control power scanner that can rapidly and efficiently scan a volume with 1000.times.1000.times.1000 or a billion points. All the previously mentioned scanner approaches can provide only 1-D or 2-D scan control capabilities. To provide the more demanding and useful 3-D scan, attempts have been made to combine these 1-D and 2-D scan devices with mechanically spinning optics such as polygons. See L. Beiser and R. Barry Johnson, "Scanners," Ch. 19, Handbook of Optics, Vol.II, Ed., M. Bass, pp. 19.1-19.57, McGraw Hill, 2nd Edition, 1995. This also means that such a scanner must have a billion degrees of freedom, a non-trivial task from a device control point of view.
The subject inventor has developed such a 3-D scanner based on simple digital control and binary properties of polarization based thin-film optics. See N. A. Riza, "High speed inertialess ultra-high space bandwidth product optical scanners using planar polarization optical devices," ARO True 3-D Displays Workshop Presentation, Orlando, Fla., Dec. 11, 1997; and N. A. Riza, "BOPSCAN Technology: A methodology and implementation of the billion point optical scanner," OSA Topical Meeting, International Optical Design Conference, SPIE Proc. 3482, June 1998. To the best of the inventor's knowledge, no other device is known for adequately solving the problems presented above. Birefringent optics, particularly bulk crystals, have been around for many years and various polarization-based switching systems have been implemented. See L. Liu and Yao Li, "Free Space optical shuffle implementations by use of birefringence-customized modular optics," Applied Optics, Vol. 36, No. 17, Jun. 10, 1997; F. Xu, J. E. Ford, and Y. Fainman, "Polarization selective computer generated holograms: design fabrication, and applications," Applied Optics, Vol. 34, No. 2, Jan. 10, 1995; T. W. Stone and J. M. Battiato, "Optical array generation and interconnection using birefringent slabs," Applied Optics, Vol 33 No. 2, Jan. 10, 1994; N. A. Riza, "Polarization based fiber-optic delay lines," SPIE Proc. Vol. 2560, p. 120-129, July 1995; and L. H. Domash, Y. M. Chew, B. Gomatam, C. Gozewski, R. L. Sutherland, L. V. Natarajan, V. P. Tondiglia, T. J. Bunning, and W. W. Adams, "Switchable-focus lenses in holographic polymer dispersed liquid crystals,"SPIE Proc., Vol. 2689, PP. 188-194, 1996. See T. W. Stone, M. S. Malcuit, J. A. Kleinfield, and J. Kralik, "Micro-optic photonic time shifters based on switched gratings," SPIE Proc. Vol. 3160, pp. 17-26, 1997; and K. Noguchi, "Optical free-space multichannel switches composed of Liquid Crystal Light Modulator Arrays and birefringent crystals," IEEE Journal of Lightwave Tech., Vol. 16, No. 8, Aug. 1998.
However, no polarization-based system using birefringent optics and digital control has been proposed for inertialess motion or scanning of light in full 3-D. The proposed invention deals with the inertialess 3-D scanner that takes advantage of polarization sensitive thin film optics to form a compact LEGO style planar stacked low control power, reversible, broad optical wavelength band, digitally controlled structure for high spaced bandwidth products (SBWP) scanning.